This invention relates to a method for the manufacture of adsorbates for use in drug delivery systems and to the adsorbates and drug formulations thereby obtained.
It is frequently desirable to delay the release of an active substance from a pharmaceutical formulation in vivo. For example, it may be desirable to delay release of the active substance within the body so that the active substance is released at a particular target site. Various coated tablets are available which are resistant to gastric juices but which are readily soluble in the higher pH environment of the small intestine. Various controlled absorption pharmaceutical formulations are also available which have a particular dissolution pattern, resulting in a controlled absorption of the active substance and, therefore, more effective medication.
The use of many active substances in therapy is complicated by solubility problems and this is especially the case with the dihydropyridine group of drugs. Drugs of the latter type such as nifedipine are very poorly soluble in aqueous media and, whilst co-precipitates thereof with certain polymers are known to improve solubility, said co-precipitates normally require a polymer to active drug ratio exceeding 3:1 in order to be effective in producing products characterised by high bioavailability with prompt peak blood levels.
Pharmaceutical formulations based on an adsorbate of a drug within a cross-linked polymer, such as cross-povidone, are also known. Furthermore, solid, rapidly absorbable medicament formulations comprising a dihydropyridine, polyvinylpyrrolidone with an average molecular weight of 15,000 to 50,000 and cross-linked insoluble polyvinylpyrrolidone are known from EP-A-0 167 09. Such formulations are rapidly absorbable and as such must be administered three or four times daily to achieve effective therapeutic levels of the active ingredient.
It is an object of the present invention to provide a sustained release capsule or tablet formulation for once daily administration wherein the bioavailability of an otherwise poorly bioavailable active substance is enhanced and effective controlled release formulations thereof can be produced.